At the time of manufacturing a base, it is desired that a metal pin retaining force (a pin torque of the base) of a base body be within a range of 0.10 Nm to 0.12 Nm. When the retaining force is less than 0.10 Nm, failure may occur such as dropping of a pin. On the other hand, if the retaining force is greater than 0.12 Nm, the pin torque can be kept a sufficient value; however, a crack of the base may frequently occur when the pin is inserted, and much chaff may be generated from peeled base resin, which causes an adverse effect on the productivity.
In addition, to make the metal pin retaining force (a pin torque of the base) of the base body stay within the range of 0.10 Nm to 0.12 Nm, a method is taken in which a rate Dh/Dp of a hole diameter Dh and an outer diameter Dp of the pin is kept within a range of 0.96 to 0.98 when the pin is inserted by press-fitting, and glass filler, which is used as a reinforcement member, is kept within a range of 5 wt % (percent by weight) to 30 wt %.
To keep the metal pin retaining force of the base body at the time of manufacturing the base within the range of 0.10 Nm to 0.12 Nm and to attain other characteristics (heat resistance, incombustibility, colorfastness, etc.) required for the base of the fluorescent lamp, such as optimal selection of resin or optimization of compounding ratio of pigment, etc. have been conducted. For example, heat resistant polybutylene terephtbalate (PBT), polyethylene terephthalate (PET), etc. are selected as thermoplastic resin, and further, white pigment such as titanium oxide is added to keep a good appearance of the base and to prevent discoloring due to the heat generated by burning. The white pigment of 5-10 wt % is added to make body colr of the base body white and prevent discoloring due to high temperature, etc.
Further, JP08-273602 discloses technique to color a resin case containing a burning circuit in dark color.
In the conventional art, there sometimes occurs a problem that even if the base body has a sufficient metal pin retaining force at the time of manufacturing the base, the pin drops at the time of attaching/removing the lamp to/from a luminaire in the market. It is known that such a problem occurs more frequently at the end of life (burning time: approximately 10,000 hours) of the fluorescent lamp.
Therefore, the present invention aims to, from an initial stage of using a fluorescent lamp to the end of the life of lamp, prevent the lamp from falling from a luminaire because a pin drops when the lamp is attached/removed to/from the luminaire and while the lamp is burned.